Devices called Y nozzles are employed to atomize heating oil (U.S. Pat. No. 2,480,459). Slightly superheated atomization fluid is forced at a constant pressure of 10 to 11 bars out of the nozzle and into the combustion chamber through several bores oriented at a specific angle. Before exiting, the fluid is contacted with the oil in the slightly wider stem of the Y. The expanding fluid bombards the oil into tiny droplets.
Special devices called premix nozzles for atomizing heavy heating oil are also known. The oil enters a liquid-fuel and atomization-fluid mixing chamber through a central pipe. Separate bores that convey atomization fluid also enter the fuel-and-fluid mixing chamber more or less at tangents. The fluid phases are similar to those that occur in a Y nozzle. The oil and atomization fluid are turbulently blended in the mixing chamber and open into the combustion chamber at a specific angle.
The bores that open into the liquid-fuel and atomization-fluid mixing chamber in a known premix nozzle (VGB Kraftwerkstechnik 56 [1956], 622-29) are Y nozzles. The bores that open out of the fuel-and-fluid mixing chamber are distributed along two arcs of a circle. The axes of the bores along each arc are at the same angle to the longitudinal axis of the atomizer. Another known premix nozzle (German Patent 3 442 148) employs a series of two mixing chambers. The bores that open out of the downstream chamber have graduated diameters and are asymmetrical to the longitudinal midplane. These features allow discontinuous supply of oil to the combustion chamber. Due to increasing demands for decreased emission of pollutants and to the decreasing quality of heating oil, known premix nozzles do not atomize the fuel adequately.